Oil burner heads adapted to burn gaseous fuels instead of oil are well known. The adaptation is usually performed by a manifold which envelopes the burner head and introduces the gas into the air flow through the burner well upstream of the oil nozzle. The manifold is simply left in place when burning oil. Oil burner heads have also been adapted to burn pulverized coal either alone or in combination with oil and /or gaseous fuel but, so far as is known, a separate "coal head", as it were, has been employed for that purpose simply mounted at the downstream end of the oil head. Essentially such coal heads are a scroll or a scroll mounted about a short tube, a mixture of pulverized coal and a portion of the primary air being blown into the scroll. The mixture enters the combined air streams emitted from the oil head through a circle of ports fed from the scroll. Several disadvantages ensure from that arrangement.
First, since owing to its radiant heat properties a refractory ignition port or tuyere most always must be used downstream of the burner, oil burner heads adapted to burn coal are most always of the refractory type. Hence the tuyere and burner head itself must be relocated to allow insertion of the coal head. Second, combustion of the coal is rather uneven and inefficient because most of the coal tends to collect at the far end of the scroll and so enters the burner's air stream through the port or two at that end of the scroll rather than from the scroll uniformly through all the ports into the burner's air stream. That results in most of the coal impinging upon the combined air streams in a more or less single transverse direction rather than in a multitude of such directions all converging at the center of the air stream. Third, the fact that the coal joins the combined primary and secondary air streams also results in less efficient mixing of the coal and air and thus less efficient combustion than if the coal were first thoroughly mixed in the primary air stream, as in the case of oil, before being combined with the secondary air.
Thus the primary object of the present invention is an adapter which allows conversion of an oil burner head to pulverize coal but obviates the disadvantages mentioned.